The present invention pertains to building materials in the form of panels or strands which are referred to herein as woodstone panels or strands and which have excellent dimensional stability that are produced by compression and hardening by heat of a mixture of a wood filler consisting predominantly of wood chips, inactive diatomaceous earth, finely divided calcined magnesite, and an aqueous solution of magnesium chloride, as well as processes for their production.
Although petrified wood is also referred to as woodstone, it is to be understood that woodstone, as the term is used herein, refers only to building materials such as are specifically described herein.
The term chipboard that is used herein, which is generally referred to as a paperboard made from waste paper, is used herein to refer to panels or boards made from sawdust or wood chips that have been bound together with binders consisting of conventional synthetic resins, which the woodstone building materials of the present invention closely resemble.
Although wood chips and sawdust are referred to herein as wood fillers, they actually are the principal components that are bound together with a binder to produce the woodstone and are to be understood as such. Sawdust, when referred to herein, refers only to the dust or particles produced in sawing wood.
Many processes for the production of woodstone building materials, which are also known as xylolith and xylolite boards or sheets, are known. In such prior processes, finely divided calcined magnesite, which is a so-called light or very bulky form of magnesium oxide or magnesia, in contradistinction to so-called heavy magnesium oxide or the dense form of magnesium oxide, is mixed together with twice or three times its volume of wood filler and an aqueous solution of magnesium chloride and the mixture thus prepared is molded into a desired shape and compressed in a compression-molding press. Woodstone panels produced in this manner, however, require very long periods for hardening or setting and do not have adequate dimensional stability.
In order to overcome these disadvantages, various alternative processes have been proposed, which however have not achieved any marked commercial success.
A process for the production of woodstone panels is also described in German Pat. No. 808,570, in which a mixture of calcined magnesite and fillers in a ratio by weight between 3:1 and 4:1, respectively, is mixed with as little mixing liquid as is necessary to produce a mixture that before compression is a powdery mass that does not cohere and which, upon compression, releases no or only a small amount of the mixing liquid. The mixture thus prepared is then compressed under a pressure between 20 and 40 kilograms per square centimeter and heated to the boiling point of the mixing liquid. The mixing liquid that is used is a highly concentrated aqueous solution of magnesium chloride (density 1.26 to 1.34 grams per liter, which is equivalent to more than 30.degree. Baume) or magnesium sulfate (density 1.20 to 1.26 grams per liter) or both. This process is however very expensive and yields only woodstone panels of high density which are neither self-supporting nor capable of retaining screws.
In U.S Pat. No. 1,443,097, a process is described for the production of a building material from a mixture consisting of sawdust, magnesium oxide and an aqueous solution of magnesium chloride. In this process the sawdust is saturated with a solution of magnesium chloride having a specific gravity from 1.16 to 1.26 at 15.degree. C., which is equivalent to a solution containing 18 to 29% by weight of MgCl.sub.2. The excess solution is then squeezed from the sawdust saturated therewith and magnesium oxide in an amount equal to the weight of magnesium chloride therein, or up to 5 times that amount is then mixed therewith. The mixture is then molded into the desired shape and allowed to set without compression or heating. The product is said to consist of about 90% by volume of wood filler corresponding to a weight ratio magnesium oxide to wood filler of about 1:2.4. Building boards of this type, however, are neither self-supporting nor dimensionally stable nor incombustible and fire-retardant.
In U.S. Pat. No. 3,788,870 are disclosed xylolith building boards and sheets made by shaping and hardening without pressure a mixture of calcined magnesite, wood filler, and an aqueous magnesium chloride solution having a specific gravity of 10.degree. to 15.degree. Baume which is equivalent to a solution containing between approximately 8.5 and 13.3% by weight of MgCl.sub.2. The hardened mixture has a ratio of magnesium oxide to wood filler between 1:1 to 1:1.5 and a ratio of magnesium oxide to magnesium chloride between 2:1 and 4:1 and may also contain inactive diatomaceous earth.
Such building boards and sheets can be made by mixing together into a plastic mass one volume of a finely divided mixture of calcined natural and synthetic magnesite with from 2 to 2.7 volumes of a magnesium chloride solution having the specific gravity specified hereinbefore, and between 4.5 to 6.2 volumes of wood filler. This mixture is allowed to swell for 45 and 90 minutes, then shaped in an open mold, dried without compression for 4 hours at a temperature between 30.degree. and 40.degree. C. and then removed from the mold and allowed to dry for a further period of at least 24 hours at a temperature between 50.degree. and 60.degree. C. Although the woodstone panel thus produced is self-supporting and incombustible and has improved dimensional stability there are still certain improvements of the mechanical properties desirable and the process due to the relatively long hardening was found to be unsuitable for commercial production.